This application relates to a flushable metering pump assembly. More particularly, this application relates to a flushable, metering pump assembly of the positive displacement, gear-type.
The positive displacement, gear-type metering pumps to which this invention relates are typically used to supply measured or metered amounts of fluid. They generally comprise gear means having two cylindrical gears disposed in a pump housing with the gears being adapted to rotate such that the gear faces intermesh and form a seal which separates inlet and outlet chambers of the pump. The gears are disposed in the pump housing such that metered amounts of fluid can be carried between the gear faces of the gears and the wall of the pump housing as the gears rotate, thus carrying the fluid from the inlet chamber of the pump to the outlet chamber of the pump. Such metering pumps are useful in those instances where materials must be delivered in measured amounts per unit time, and are particularly useful where two or more components must be delivered in measured amounts per unit time to prepare a composite material. In those cases, various feed lines delivering the various components may each flow through or be connected with a metering pump which meters the amount of fluid flowing through that line to the manifold or other means where the materials are combined.
One type of such system requiring metered amounts of two or more materials is a paint system employing multicomponent paint materials which must be combined just prior to application to a substrate. For example, two component paint systems based on polyurethanes which require one component containing a hydroxy functional resin and another component containing an isocycanate crosslinker must be combined just prior to application of the substrate because the components would react prematurely if combined earlier. The materials must be combined in precise amounts and therefore the two components must be metered as they pass to the spray gun where they are combined just prior to application to substrate.
In paint applications systems employing two component paints, such as those discussed above, a problem arises in connection with color changes which must frequently be made during painting operations, particularly those involving painting of automobiles. When a color is changed, it is necessary to flush the lines and the spray gun in order to avoid contamination of the color to be subsequently applied. In those cases where a metering pump is present in the common feed line for the component containing pigment, the metering pump must also be flushed. This flushing of a paint line, generally accomplished by high pressure introduction of gas and/or solvent, must be accomplished rapidly in order to accomplish a rapid color change. Unless the high pressure gas and/or solvent is allowed to at least partially bypass the metering pump, the speed of flushing is seriously impeded. Even in those instances where a multi-speed pump motor is employed so that the RPM of the pump may be increased so as to accommodate more rapid flow of solvent during the flushing cycle, the speed and thoroughness of the flushing are not adequate to allow rapid color change. The result is that in order to accomplish the degree of flushing of the pump and thereby avoid contamination of the paint, it is necessary to employ a greater flushing cycle period than is practical for assembly line operations. In addition, the operating life of a precision metering pump will be drastically shortened if it is operated at a high RPM with low lubricity flushing of solvents or solvent/gas mixtures during flushing.
U.S. Pat. No. 3,145,930 to Herklotz et al and 3,219,273 to Killen each disclose painting systems which are adapted to be flushed prior to changing colors. While neither of these painting systems employs multicomponent paints, they do include pumps which must be flushed prior to color change. In each case, however, the pumps are driven by multi-speed motors which, as discussed above, allow the RPM of the pump to be increased during the flush cycle thus increasing the amount of solvent that may pass therethrough. See Column 1, lines 46-62 and Column 2, lines 8-17 of Herklotz et al and Column 3, lines 50-74 of Killen. U.S. Pat. No. 3,330,290 to Porter teaches a water-fertilizer mixing pump which is adapted to be flushed so as to flush and wash out any fertilizer in the fertilizer portion of the pump. See drawing and Columns 2 and 3.
U.S. Pat. Nos.: 3,155,539 to Juvinall; 3,403,695 to Hopkins; 3,450,092 to Kock; 3,458,133 to Wiggins; 3,477,870 to Boretti et al; 3,672,570 to Scarbrough et al; 3,674,205 to Kock; and 3,857,513 to Wiggins all teach paint or coating systems providing for color change. However, none of these systems employs a pump which must be flushed during the change from one color to another and thus they do not address the above problem.